Filter cartridges used for filtering fluids such as lubricating oil can be arranged with a full flow filter element and a bypass filter element, the bypass filter element being stacked on the full flow filter element with the fluid flowing radially through the filter elements into hollow cores thereof and then axially out of the cartridges.
This arrangement is widely employed to filter lubricating oil used in internal combustion engines. Engine wear, specifically piston ring wear, is directly related to the amount of actual filtration of lubricating oil by both full flow and bypass filters which is mixed after filtration. It has been found that by combining filtration provided by a full flow filter element with that of a bypass filter element substantially reduces engine wear as compared to using only full flow filtration. Moreover, by using a combination of full flow and bypass flow lubricating oil, service intervals can be increased so that maintenance expense is reduced. Maintenance expense is a major consideration in the total expense of operating a vehicle. This is, of course, is a major concern for fleets of vehicles, such as the fleets operated by trucking companies. In addition, by keeping lubricating oil clean, it can remain in engines longer and does not have to be recycled at shorter intervals. Consequently, environmental concerns due to vast amounts of used lubricating oil are reduced because less used oil must be recycled. It is therefore beneficial to enhance the performance of lubricating oil cartridges which utilize both full flow filter elements and bypass filter elements.
Arrangements have evolved wherein filter mounting bases, which are integral with engine mounting blocks, now have increased diameters with dirty inlet oil flowing though a plurality of radially positioned, spaced ports and with filtered clean oil flowing axially through a neutral outlet port. Increased diameter filter mounting bases require threaded nutplates of increased diameter which has resulted in modified filter configurations. In addition, it has been found that imparting a cyclonic rotation to dirty inlet oil increases the capacity and efficiency of the annular filter media used in the spin-on filters.
In that spin-on filter elements are designed to be replaced at specified intervals, it is worthwhile to design these filters to reduce the expense of their manufacturer while maintaining their reliability. Expense and reliability are of considerable importance with filters that may be used with diesel engines because it is necessary to change these filters at shorter intervals than filters used for gasoline engines.